Treefrogs in the suburbs: What they do, and where you might see - and hear - them

Growing up just a few miles from where I'm sitting, I had a pretty simple take on amphibians. Smooth-skinned frogs were in or near a lake. Rough-skinned toads were found in the garden or lawn. Last but not least, lizardlike salamanders lurked in the window wells. That about covered it.

When I moved back to Stillman in 1994, I literally heard from a couple of different habitats.

Chorus frogs, often mistakenly called spring peepers, chirped from the cattail marsh and the aptly named treefrogs called from the woodland. Treefrogs will be the subject for this column.

Arboreal chorus

There are two types of treefrogs that can be found in the area: Eastern gray treefrog and Cope's gray treefrog. Here's the thing - they look exactly the same. Luckily, their calls differ, and based on what I heard, we have the gray treefrog.

The breeding call is best described as a guttural trill that is similar to the song of a red-bellied woodpecker. The buzzing trill of a Cope's treefrog is higher-pitched. The treefrogs' choruses intensify during warm, humid evenings in May and June. The calls, made only by males, can be heard through much of August.

If you're lucky enough to locate a singing male, look around the nearby branches. You might notice some other quiet males, known as satellite males, alertly watching.

These are usually first-year males. These guys sometimes waylay and mate with a female coming toward the singing male.

On other occasions, after the singing male mates with a female, a satellite male takes over his location and starts singing for himself. Females favor males with the longest and most frequently repeated calls.

Original bug zappers

Treefrogs' skin is not smooth like pond frogs. Their rough skin resembles a toad's. The frogs' feet, however, are quite different. Their toes have suction cups that allow treefrogs to cling to tree trunks and house windows.

In addition, the toe pads secrete a mucous that further enhances their ability to adhere to vertical surfaces. If you live in a wooded habitat, you might see a treefrog sticking to the wall near a porch lamp.

Since treefrogs are nocturnal, an evening light is made to order. They are just waiting for some hapless, small insect to get in range of their sticky tongues. Just think of their tongues as the original bug zappers.

In winter, of course, there aren't any bugs to zap. So, eastern gray treefrogs bury themselves underneath leaves, logs, rock, and soil. They produce glycerol, which acts like antifreeze, to keep their blood from freezing. The rest of their body fluids can become frozen. In fact, roughly 40% of a treefrog's body can freeze during the winter. Suffice it to say, they put the cold in coldblooded.

Flag-waving tadpoles

After they thaw and emerge from their burrows, the little frogs make their way to the nearest pond, ditch, or wetland. That's where you'll find treefrogs depositing their eggs. They start reproducing in mid-April. The eggs are laid in clusters of 10 to 40. When done, a female can lay as many as 2,000 eggs!

They will be discovered on the water's surface near or on emergent vegetation. The wet areas used by treefrogs can be temporary or permanent, as well as natural or artificial.

Some locations, like a drainage ditch, may lack tadpole predators. Such predators would include giant water bugs, predaceous diving beetles, and dragonfly larvae. Fascinating research has shown that treefrog tadpoles in wetlands without predators have bland-colored tails.

If the tadpoles are threatened by predators, they sport a bright red tail. It appears that a gaudy tail warns predators that these tadpoles' skin contains some noxious secretions.

Speaking of tadpole mortality, it should be noted that treefrog tadpoles are particularly vulnerable to the insecticide carbaryl. Bright tails don't discourage toxic chemicals.

Camouflage and color

Treefrogs aren't very big. After spending one to two months as tadpoles, the adult frogs will range in size from 1.25 to 2.25 inches long. Females are slightly larger than males. Like the tadpoles, the adults can be dramatically different in color. Sometimes they are gray, looking like little patches of lichen on a tree trunk. Other times, they are mottled green. The young adult frogs are often a solid emerald green.

In order to match the surface they are on, treefrogs can change from green to gray or brown in roughly an hour varying with environmental factors such as humidity and temperature. The dusky tones are more common when it is cold or dark out. Regardless of the frog's cryptic coloration, you will note a small white patch under the eye. Also, a male will have a dark throat while the female's throat is light.

Be aware that their throats can be next to impossible to see. Treefrogs make a point to flatten their bodies against the substrate they are clinging to. By doing so, it is thought, they are less likely to cast a shadow and be noticed by a hungry snake or bird. If they successfully keep themselves hidden, treefrogs might live to be 7 years old.

Equal time for Midwest treefrogs

If you search online for treefrogs, you will be overwhelmed with information about rainforest species. I know the tropical treefrogs are appealing and colorful and their habitat is disappearing.

Still, how about a little appreciation for our - what should I call them - snow forest species?

Midwestern treefrogs have to withstand summer droughts and being frozen in winter. Could tropical treefrogs survive that? Maybe I'm a bit envious of all that equatorial biodiversity.

With that diversity in mind, would it be too much to ask the Cope's gray treefrog and eastern gray treefrog to actually look different? Just saying.

• Mark Spreyer is executive director of the Stillman Nature Center in Barrington. Email him at stillnc@wildblue.net.